Field of the Invention
The invention relates to an adapter fitting for use in a stationary gas turbine installation having a compressor, a turbine, a combustion chamber and an external pressure-supercharged fluidized-bed furnace, the adapter fitting having:
a housing which can be fitted between a combustion-chamber connection flange and a combined connection flange for process air compressed by the compressor and for flue gas being discharged toward the turbine, PA1 a first line connection at the housing for fitting to the combined connection flange, with an inlet for process air compressed by the compressor and with an outlet for the flue gas, and PA1 a second line connection at the housing for fitting to the combustion-chamber connection flange, with an inlet for the flue gas emanating from the combustion chamber and with an outlet for the process air compressed by the compressor. PA1 High NO.sub.x levels are to be expected with combustion using hot combustion air. PA1 Difficulties arise with the combustion, on one hand, of natural gas and, on the other hand, of low calorific value coal gas using a single combustion chamber which is operated with a high air inlet temperature. PA1 The fluidized-bed flue gas may entrain ash particles which, upon passing through the flame during the addition of the coal gas, may melt. PA1 Complex hot-gas fittings are required. PA1 It is difficult to protect the gas turbine from running up unintentionally as a result of fluidized-bed flue gases.
Such an adapter fitting is known from an article entitled "Die Standard-Gasturbine im Druckwirbelschicht-Einsatz" [The Standard Gas Turbine in Pressurized Fluidized-Bed Mode] by F. Stuhlmuller et al., in VGB Kraftwerkstechnik (1995), Volume 12, Pages 1037-1042 or from UK Patent Application GB 2 017 219 A.
Conventional gas turbines in which a pressure-supercharged fluidized-bed furnace is used instead of the combustion chamber to generate the hot flue gas are suitable for use in power plants. For that purpose, it is possible to use conventional gas turbine installations with two externally flanged-on combustion chambers. In that case, in order to connect the gas turbines to the pressure-supercharged fluidized-bed furnace system, it is merely necessary to remove the two combustion chambers and replace them with a connection fitting for the fluidized-bed furnace system. That connection fitting may, for example, be a concentric double-tube configuration, in which the flue gas emanating from the fluidized-bed furnace is guided in an inner tube to the gas turbine, while in an outer annular space the compressed process air generated by the compressor of the gas turbine installation is guided to the fluidized-bed furnace system.
The disadvantage of the low turbine inlet temperature of the flue gas in such fluidized-bed systems is eliminated by a further development, in which some of the coal being introduced is gasified, and the low calorific value combustion gas is used for further heating of the fluidized-bed flue gas before it enters the turbine.
In tried-and-tested configurations of such a gas turbine with a pressure-supercharged fluidized-bed furnace, the low calorific value combustion gas is added at a high temperature level, in such a way that the hot flue gases from the pressurized fluidized bed are mixed with compressed air from the compressor outlet of the gas turbine installation and are used as combustion air. The air inlet temperature at those burners is approximately 760.degree. C.
Various problems arise because of that configuration:
The prior art has already developed burner types which are constructed for the combustion of low calorific value synthesis gas using hot combustion air while at the same time achieving acceptable NO.sub.x emissions. However, the problems of melting ash particles, with the use of complex hot-gas fittings and the heat losses caused by the use of concentric tubes through the cooling of the internally guided flue gas, have remained unsolved.